Each signature page shall contain an affidavit made and executed by the individual in whose presence all of the signatures on that page were affixed and who observed each of those signatures being affixed. The affidavit shall contain the statements, required by regulation, designed to assure the validity of the signatures and the fairness of the petition process. A circulator must be at least 18 years old at the time any of the signatures covered by the affidavit are affixed.